In the construction industry, structures (such as walls, floors, slabs and columns) of concrete are produced by positioning reinforcing such as steel reinforcing bars in a region where concrete is then poured to produce the structure. The bars are supported in desired positions and often there is a need to join length of bars to each other to ensure that the reinforcing not only is correctly positioned, but is able to transmit load across the coupling so that the bars can accommodate a large part or even their full axial capacity in either tension or compression.
In the past, wire ties or wraps have been secured around overlapping ends of adjacent bars to hold them relative to one another prior to the concrete pour. Axial loads are transferred from one bar to the other overlapped bar through the concrete encasing the two joined bars. This method uses more bar than necessary as the overlapped length of bar is only useful to effect the transfer of axial loads and these overlapping lengths can form a significant mass of reinforcing bar in a structure.
In another arrangement, bars are formed with short externally threaded end portions and a sleeve with left handed and right handed internal thread portions is used to allow adjacent end of the bars to be connected to one another.
The formation of the external threaded portions on ends of the bars results in those ends being of less diameter than the remainder of the bar and thus is undesirable since engineering requirements may dictate that a bar having a predetermined diameter is used. One way to overcome this difficulty is to employ oversized bars. This ensures that the threaded end of the bar is still of a diameter equal to or greater than the diameter dictated by the engineering requirements. However, with this arrangement, most of the bars are of a gauge greater than is necessary.
Ideally the properties of the coupling, such as its axial capacity and its ductility, are at least the same as the major portion of the bars and that only limited longitudinal slip will occur when the coupling is loaded. If these properties are not within certain tolerances, then the coupling can significantly compromise the resulting structure. For example, if there is excessive longitudinal slip then this can cause excessive localised cracking thereby heightening the risk of corrosion, and may also cause excessive deflection. If the coupling is not as ductile as the main part of the bar, then this can cause localised stress concentration which potentially could result in catastrophic failure of the coupling.
The use of separate coupling elements, such as the threaded sleeve mentioned above, may be problematic where a construction site has reinforcing bars of different strength as there is a danger of a potential mismatch of the sleeve to the bars. Furthermore, the use of a threaded arrangement requires for there to be some play between the components to enable easy installation, which in turn may result in unacceptable longitudinal slip under load. Also there is an ongoing risk that the couplings are not adequately tightened on site which will compromise the coupling.
In the Applicant's earlier International application WO 2006/094320, a reinforcing bar is disclosed which includes an enlarged termination integrally formed on the reinforcing bar shaft. The termination is profiled to include locking formations that enable the termination to form part of an interlock and is disclosed as been made by deforming an end of the reinforcing bar. A process of forming the reinforcing with the profiled termination is disclosed in International application WO 2006/084321, where the reinforcing bar end is subjected to various forging and milling stages. Whilst the reinforcing disclosed in these earlier applications performs well, the specialised equipment required to manufacture the reinforcing provides a constraint to distributed manufacture of the product in view of the necessary capital outlay for that equipment. Accordingly, alternative modes of manufacturing the reinforcing are desirable.
A reference herein to prior art is not an admission that the prior art forms part of the common general knowledge of a person of ordinary skill in the art in Australia or elsewhere.